1. Field of the Invention
The present invention relates generally to a radio transceiver. More particularly, the present invention relates to an analog baseband filter constituting a Radio Frequency Integrated Circuit (RFIC) of a multi-mode multi-band radio transceiver.
2. Description of the Related Art
A Radio Frequency Integrated Circuit (RFIC) may be an integrated circuit that operates in a range of radio frequencies ranging from about 300 MHz to about 30 GHz, and the RFIC is used in mobile phones, notebook computers, smart phones, Bluetooth products, and the like. Lately, RFICs should be manufactured in a small size and to operate with low power in order to increase a battery life of mobile terminals while supporting various communication protocols used in Second-Generation (2G), Third-Generation (3G), Fourth-Generation (4G) communication networks, and the like on a single chip. In order for the RFIC to have a small size, functions of blocks included in an RFIC should be integrated in order to reduce the number of blocks and to minimize current consumed by each block. However, in communication systems in which 16-Quadrature Amplitude Modulation (QAM) (16QAM) or 64QAM is used in order to process a large amount of data, like in a Long Term Evolution (LTE) communication network, it is difficult to reduce current consumption and the circuit area while ensuring performance required by the 16QAM or 64QAM.
FIG. 1 illustrates a structure of a transmission (TX) chain of a RFIC according to the related art.
Referring to FIG. 1, the TX chain of the RFIC includes a baseband modem 110, an analog baseband 120, and a Radio Frequency (RF) front-end 130. The analog baseband 120 includes a Current-to-Voltage (I-V) converter 121, a Power Gain Amplifier (PGA) 122, a Ramping Variable Gain Amplifier (RVGA) 123, and a Low Pass Filter (LPF) 124.
The I-V converter 121 converts a current received from the baseband modem 110 operating in a current mode into a voltage, and the PGA 122 attenuates the received signal by a predetermined gain. The PGA 122 and the RVGA 123 have a gain/dynamic range of −30 dB to 0 dB and of −50 dB to 0 dB, respectively, according to received codes. Then, the LPF 124 removes images and noise from the input signal and transfers the resultant signal to the RF front-end 130. There have been various efforts and proposals for reducing the current consumption and size of an RFIC, and one of the proposals is an integrated circuit of an I-V converter and a PGA.
FIG. 2 illustrates a structure in which an I-V converter is integrated with a PGA according to the related art.
Referring to FIG. 2, functions of the PGA are implemented by connecting switches and resistors to the I-V converter in a multi-stage fashion. However, due to a property of the resistor wherein resistance depends on a temperature, the structure illustrated in FIG. 2 may have a problem that a common mode voltage varies and Local Oscillator (LO) leakage occurs when a temperature changes after Direct Current (DC) offset calibration.
FIG. 3 illustrates a PGA structure according to the related art.
Referring to FIG. 3, a structure which ensures a gain/dynamic range with a PGA that uses an active device is illustrated, and a gain value is determined according to a resistance ratio of resistance R1 to resistance R2. However, since the PGA structure of FIG. 3 includes an Operational-Amplifier (OP-AMP) which is an active device, the PGA structure may consume a large amount of current and occupy a wide area.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.